Abstract
This paper presents a method for ultimate strength design of structural frame, which is based on the equilibrium conditions of external and internal force. The outline of the method is as follows: Combining two groups of equilibrium equations which consist of those of vertical and horizontal direction, according to the type of the mechanism of the frame, we obtain the plastic moment carrying capacity of each members as a function of the external load. In this process we must check the moment of the each members to satisfy the plastic moment conditions. The special feature of this method is the establishment of direct relations between the external load and the plastic moment of each members, and we can aquire a series of the plastic moments correspond to any type of the mechanism. The fact is usefull in the design of requlally framed structures. We illustrate this theory in the treatment of portal frame and also investigate on the minimum weight design of the frame, according to the linear approximating theory.
